Strongly Coupled Coherent Phonons in Single-Layer MoS2

• Published in: ACS nano 2020-05, Vol.14 (5), p.5700-5710
• Main Authors: Trovatello, Chiara, Miranda, Henrique P. C, Molina-Sánchez, Alejandro, Borrego-Varillas, Rocío, Manzoni, Cristian, Moretti, Luca, Ganzer, Lucia, Maiuri, Margherita, Wang, Junjia, Dumcenco, Dumitru, Kis, Andras, Wirtz, Ludger, Marini, Andrea, Soavi, Giancarlo, Ferrari, Andrea C, Cerullo, Giulio, Sangalli, Davide, Conte, Stefano Dal
• Format: Article
• Language: English
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.0c00309

We present a transient absorption setup combining broadband detection over the visible–UV range with high temporal resolution (∼20 fs) which is ideally suited to trigger and detect vibrational coherences in different classes of materials. We generate and detect coherent phonons (CPs) in single-layer (1L)-MoS2, as a representative semiconducting 1L-transition metal dichalcogenide (TMD), where the confined dynamical interaction between excitons and phonons is unexplored. The coherent oscillatory motion of the out-of-plane A′1 phonons, triggered by the ultrashort laser pulses, dynamically modulates the excitonic resonances on a time scale of few tens of fs. We observe an enhancement by almost 2 orders of magnitude of the CP amplitude when detected in resonance with the C exciton peak, combined with a resonant enhancement of CP generation efficiency. Ab initio calculations of the change in the 1L-MoS2 band structure induced by the A′1 phonon displacement confirm a strong coupling with the C exciton. The resonant behavior of the CP amplitude follows the same spectral profile of the calculated Raman susceptibility tensor. These results explain the CP generation process in 1L-TMDs and demonstrate that CP excitation in 1L-MoS2 can be described as a Raman-like scattering process.